The instant invention relates to sensing devices and more particularly relates to photoelectric sensor apparatus for sensing the absence of filament on the supply bobbins of machinery, such as braiding machines, knitting machines and the like.
Photoelectric, opto-electric and mechanical filament sensors for machines have heretofore been known in the art. For convenience, the term filament is used herein to include generically similar materials such as natural or synthetic yarn, cord, string, wire, etc. Filament sensors are used in various types of textile machines to detect the presence or absence of a filament as it passes through a particular part of the machine so that the machine may be shut-down when there is no longer any filament available on one of the supply bobbins or where there is a break in the filament. Mechanical sensing means have previously been known whereby when a bobbin becomes empty, braking means are operated for stopping the machine. The problem with these mechanical sensing means is that they are conventionally triggered by the terminal end of the filament breaking free from the bobbin, which causes the filament to become snarled into what is known as a "rats nest", which takes time and expense to untangle before the machine can again operate.
The U.S. Pat. Nos. 3,158,852 to Schacher; 4,023,599 to Zeleny; 4,341,958 to Ohsawa; 4,365,654 to Viniczay et al; and 4,753,149 to Celani are illustrative of the various photoelectric and opto-electric filament sensors that have heretofore been known in the art. The patents to Schacher, Ohsawa, Viniczay et al and Celani teach the use of photoelectric sensors which are operable for detecting the presence or absence of filament which is passing continuously through a given region in a textile machine. The sensors output a signal to operate a warning light or buzzer, or to stop the operation of the machine when thread is absent. The Zeleny patent teaches an opto-electronic weft yarn detector for a weaving machine. The detector passes radiation across the path of the yarn onto radiation detectors to sense if the yarn is being supplied correctly. If a problem in the supply of yarn is detected, the detector emits a signal to shut-down the machine or to signal a warning buzzer or light. It has been found that these types of detectors also suffer from the same tangling problem associated with mechanical sensors because the terminal end of the filament breaks free from the bobbin and forms a tangle before the machine is shut-down.
Filament sensors are of particular importance in braiding machines wherein a plurality of bobbins constantly spin around the axis of the machine while spinning around their own axis. Because of the multitude of filaments, and the manner in which these machines operate, it is difficult to employ filament sensors. In this regard, there have been known in the art photoelectric bobbin feelers which respond when a supply bobbin becomes empty in which event the machine is stopped. Two examples of photoelectric bobbin feelers are described in the U.S. Pat. Nos. 3,892,492 and 4,276,910 to Eichenberger, wherein one or more light sources direct light onto the core of the bobbins, and one or more photoelectric sensors are utilized to discriminate between the different patterns of diffuse and specular light which are reflected off of the surface of the full and empty bobbins. There have been distinct problems however, in adjusting these types of sensors to the many different patterns of light reflected from different types of bobbins and different types of filament windings. Because of these problems, the heretofore available photoelectric bobbin feelers have not been found to be totally satisfactory.